A circulating complex between ASAT and IgG in serum in an apparently healthy woman

Aspartate aminotransferase-immunoglobulin complexes in patients with chronic liver disease

AIM: To determine the complex of AST and immunoglobulin and to investigate its clinical significance in patients with liver disease.

METHODS: The complex of AST and immunoglobulin was determined by encounter immunoelectrophoresis and its clinical significance was investigated in 128 patients with liver disease.

RESULTS: AST was bound to immunoglobulin of anti-immunoglobulin A (IgA) class, but any binding to anti-immunoglobulin G and anti-immunoglobulin M classes was not observed. Although the incidence of AST–immunoglobulin complex was 41.8% in chronic hepatitis (CH), the incidences in liver cirrhosis and hepatocellular carcinoma were 62.2 and 90.0%, respectively. In alcoholic liver disease with high level of serum IgA, the incidence of the complex was 66.7%, which was higher than that in CH. The ratio of binding to lambda-chain of IgA was higher than that to kappa-chain of IgA. The serum level of IgA and the ratio of AST/alanine aminotransferase (ALT) were significantly higher in patients with AST–IgA complex than in those without complex.

CONCLUSION: These results suggest that AST–IgA complex in patients with progressive liver diseases and alcoholic liver injury can lead to elevation of the ratio of AST/ALT.

Macro-aspartate aminotransferase in a female with antibodies to hepatitis C virus

Persistent elevation of aspartate aminotransferase (AST) activity in serum due to the presence of a macroenzyme form of AST (macro-AST) may lead to diagnostic confusion in many clinical conditions, particularly those associated with chronic liver disease. We describe a case of macro-AST arising in an adult female with a false-positive hepatitis C virus (HCV) RNA test result that was not accompanied by other biochemical or histologic evidence of liver disease. The presence of macro-AST in serum was confirmed utilizing size-exclusion, high performance liquid chromatography (HPLC) and Protein G-agarose beads to precipitate immune complexes of AST and immunoglobulin G followed by centrifugation and AST activity measurements in the supernatant. A brief review of the clinical enzymology of AST and methods used to quantify serum macro-AST activity is provided.

Macroenzyme investigation and monitoring in children with persistent increase of aspartate aminotransferase of unexplained origin

Ten children with asymptomatic persistent cryptogenic increased serum levels of aspartate aminotransferase (AST) were screened for detection and monitoring of AST macroenzyme (macroAST). MacroAST was found in 4 patients; their serum AST levels were significantly higher than in those without biochemical evidence of macroAST (mean +/- SD: 515 +/- 433 and 78 +/- 16 IU/L, respectively; P = .0095). MacroAST was a persistent, benign phenomenon and was probably not congenital.

Highly elevated lactate dehydrogenase level in a healthy individual: a case of macro-LDH

Macroenzymes are complexes of serum enzymes with a plasmatic protein. They have a higher molecular weight and a more prolonged serum half-life than those of unbound enzymes. Although macroenzymes may be found in the serum of post-myocardial infarction patients, they are not usually associated with any specific disease. Their presence, however, can cause an elevation in the serum levels of an enzyme, possibly leading to errors in diagnosis. We report a patient with extremely elevated serum levels of lactate dehydrogenase (LDH) due to the formation of complexes with immunoglobulin G. She had undergone a myriad of clinical examinations until the macroenzyme responsible for this finding was detected. We also review the literature on the clinical significance of macro-LDH. We propose that awareness of this rare and probably benign phenomenon can spare the patient from the distress of exhaustive investigations.

Aspartate aminotransferase isoenzymes

Aspartate aminotransferase (AST, EC 2.6.1.1) exists in human tissues as two distinct isoenzymes, one located in the cytoplasm (c-AST), and the other in mitochondria (m-AST). Striated muscle, myocardium, and liver tissues are the main sources of AST. A growing body of information suggests that determination of AST isoenzymes in human serum is useful in evaluating damage to some of these organs. In hepatic disease, the test is used to assess liver necrosis and for determining prognosis. It may also assist in identifying patients with active alcoholic liver disease. In patients with acute myocardial infarction, measurement of AST isoenzymes provides diagnostic information that differs from that obtained by determination of total creatine kinase and lactate dehydrogenase enzymes, and their isoenzymes.

Immunoglobulin-AST complex

A case of AST-IgG complex presenting as an isolated AST elevation is described. Measurement of elevated serum AST activity is dependent upon the inclusion of pyridoxal 5-phosphate in the substrate.

Investigation of a persistently raised serum AST

The AST responsible for a raised enzyme activity, with otherwise normal biochemistry, in a single individual over a 16-month period has been characterized as an IgG (lambda)-AST complex by (i) estimation of the molecular size by gel exclusion chromatography on Sephadex G200, (ii) agarose gel electrophoresis, (iii) immunoprecipitation by anti-immunoglobulin antisera and (iv) adsorption on to protein A-agarose.